A Matrix Based Approach for Color Transformations in Reflections

In this thesis, I demonstrate the feasibility of linear regression with 4 × 4 matrices to perform color transformations, specifically looking at the case of color transformations in reflections. I compare and analyze the power and performance linear regression models based on 3 × 3 and 4 × 4 matrices. I conclude that using 4 × 4 matrices in linear regression is more advantageous in power and performance over using 3 × 3 matrices in linear regressions, as 4 × 4 matrices allow for categorically more transformations by including the possibility of translation. This provides more general affine transformations to a color space, rather than being restricted to passing through the origin. I examine the benefits of allowing for negative elements in color transformation matrices. I also touch on the possible differences in application between filled 4 × 4 matrices and diagonal 4 × 4 matrices, and discuss the limitations inherent to linear regression used in any type of matrix operations

A Matrix Based Approach for Color Transformations in Reflections

In this thesis, I demonstrate the feasibility of linear regression with 4 × 4 matrices to perform color transformations, specifically looking at the case of color transformations in reflections. I compare and analyze the power and performance linear regression models based on 3 × 3 and 4 × 4 matrices. I conclude that using 4 × 4 matrices in linear regression is more advantageous in power and performance over using 3 × 3 matrices in linear regressions, as 4 × 4 matrices allow for categorically more transformations by including the possibility of translation. This provides more general affine transformations to a color space, rather than being restricted to passing through the origin. I examine the benefits of allowing for negative elements in color transformation matrices. I also touch on the possible differences in application between filled 4 × 4 matrices and diagonal 4 × 4 matrices, and discuss the limitations inherent to linear regression used in any type of matrix operations

Shadow segmentation and tracking in real-world conditions

Visual information, in the form of images and video, comes from the interaction of light with objects. Illumination is a fundamental element of visual information. Detecting and interpreting illumination effects is part of our everyday life visual experience. Shading for instance allows us to perceive the three-dimensional nature of objects. Shadows are particularly salient cues for inferring depth information. However, we do not make any conscious or unconscious effort to avoid them as if they were an obstacle when we walk around. Moreover, when humans are asked to describe a picture, they generally omit the presence of illumination effects, such as shadows, shading, and highlights, to give a list of objects and their relative position in the scene. Processing visual information in a way that is close to what the human visual system does, thus being aware of illumination effects, represents a challenging task for computer vision systems. Illumination phenomena interfere in fact with fundamental tasks in image analysis and interpretation applications, such as object extraction and description. On the other hand, illumination conditions are an important element to be considered when creating new and richer visual content that combines objects from different sources, both natural and synthetic. When taken into account, illumination effects can play an important role in achieving realism. Among illumination effects, shadows are often integral part of natural scenes and one of the elements contributing to naturalness of synthetic scenes. In this thesis, the problem of extracting shadows from digital images is discussed. A new analysis method for the segmentation of cast shadows in still and moving images without the need of human supervision is proposed. The problem of separating moving cast shadows from moving objects in image sequences is particularly relevant for an always wider range of applications, ranging from video analysis to video coding, and from video manipulation to interactive environments. Therefore, particular attention has been dedicated to the segmentation of shadows in video. The validity of the proposed approach is however also demonstrated through its application to the detection of cast shadows in still color images. Shadows are a difficult phenomenon to model. Their appearance changes with changes in the appearance of the surface they are cast upon. It is therefore important to exploit multiple constraints derived from the analysis of the spectral, geometric and temporal properties of shadows to develop effective techniques for their extraction. The proposed method combines an analysis of color information and of photometric invariant features to a spatio-temporal verification process. With regards to the use of color information for shadow analysis, a complete picture of the existing solutions is provided, which points out the fundamental assumptions, the adopted color models and the link with research problems such as computational color constancy and color invariance. The proposed spatial verification does not make any assumption about scene geometry nor about object shape. The temporal analysis is based on a novel shadow tracking technique. On the basis of the tracking results, a temporal reliability estimation of shadows is proposed which allows to discard shadows which do not present time coherence. The proposed approach is general and can be applied to a wide class of applications and input data. The proposed cast shadow segmentation method has been evaluated on a number of different video data representing indoor and outdoor real-world environments. The obtained results have confirmed the validity of the approach, in particular its ability to deal with different types of content and its robustness to different physically important independent variables, and have demonstrated the improvement with respect to the state of the art. Examples of application of the proposed shadow segmentation tool to the enhancement of video object segmentation, tracking and description operations, and to video composition, have demonstrated the advantages of a shadow-aware video processing

High-fidelity colour reproduction for high-dynamic-range imaging

The aim of this thesis is to develop a colour reproduction system for high-dynamic-range (HDR) imaging. Classical colour reproduction systems fail to reproduce HDR images because current characterisation methods and colour appearance models fail to cover the dynamic range of luminance present in HDR images. HDR tone-mapping algorithms have been developed to reproduce HDR images on low-dynamic-range media such as LCD displays. However, most of these models have only considered luminance compression from a photographic point of view and have not explicitly taken into account colour appearance. Motivated by the idea to bridge the gap between crossmedia colour reproduction and HDR imaging, this thesis investigates the fundamentals and the infrastructure of cross-media colour reproduction. It restructures cross-media colour reproduction with respect to HDR imaging, and develops a novel cross-media colour reproduction system for HDR imaging. First, our HDR characterisation method enables us to measure HDR radiance values to a high accuracy that rivals spectroradiometers. Second, our colour appearance model enables us to predict human colour perception under high luminance levels. We first built a high-luminance display in order to establish a controllable high-luminance viewing environment. We conducted a psychophysical experiment on this display device to measure perceptual colour attributes. A novel numerical model for colour appearance was derived from our experimental data, which covers the full working range of the human visual system. Our appearance model predicts colour and luminance attributes under high luminance levels. In particular, our model predicts perceived lightness and colourfulness to a significantly higher accuracy than other appearance models. Finally, a complete colour reproduction pipeline is proposed using our novel HDR characterisation and colour appearance models. Results indicate that our reproduction system outperforms other reproduction methods with statistical significance. Our colour reproduction system provides high-fidelity colour reproduction for HDR imaging, and successfully bridges the gap between cross-media colour reproduction and HDR imaging

CMOS optical centroid processor for an integrated Shack-Hartmann wavefront sensor

A Shack Hartmann wavefront sensor is used to detect the distortion of light in an optical wavefront. It does this by sampling the wavefront with an array of lenslets and measuring the displacement of focused spots from reference positions. These displacements are linearly related to the local wavefront tilts from which the entire wavefront can be reconstructed. In most Shack Hartmann wavefront sensors, a CCD is used to sample the entire wavefront, typically at a rate of 25 to 60 Hz, and a whole frame of light spots is read out before their positions are processed. This results in a data bottleneck. In this design, parallel processing is achieved by incorporating local centroid processing for each focused spot, thereby requiring only reduced bandwidth data to be transferred off-chip at a high rate. To incorporate centroid processing at the sensor level requires high levels of circuit integration not possible with a CCD technology. Instead a standard 0.7J..lmCMOS technology was used but photodetector structures for this technology are not well characterised. As such characterisation of several common photodiode structures was carried out which showed good responsitivity of the order of 0.3 AIW. Prior to fabrication on-chip, a hardware emulation system using a reprogrammable FPGA was built which implemented the centroiding algorithm successfully. Subsequently, the design was implemented as a single-chip CMOS solution. The fabricated optical centroid processor successfully computed and transmitted the centroids at a rate of more than 2.4 kHz, which when integrated as an array of tilt sensors will allow a data rate that is independent of the number of tilt sensors' employed. Besides removing the data bottleneck present in current systems, the design also offers advantages in terms of power consumption, system size and cost. The design was also shown to be extremely scalable to a complete low cost real time adaptive optics system

CMOS optical centroid processor for an integrated Shack-Hartmann wavefront sensor

A Shack Hartmann wavefront sensor is used to detect the distortion of light in an optical wavefront. It does this by sampling the wavefront with an array of lenslets and measuring the displacement of focused spots from reference positions. These displacements are linearly related to the local wavefront tilts from which the entire wavefront can be reconstructed. In most Shack Hartmann wavefront sensors, a CCD is used to sample the entire wavefront, typically at a rate of 25 to 60 Hz, and a whole frame of light spots is read out before their positions are processed. This results in a data bottleneck. In this design, parallel processing is achieved by incorporating local centroid processing for each focused spot, thereby requiring only reduced bandwidth data to be transferred off-chip at a high rate. To incorporate centroid processing at the sensor level requires high levels of circuit integration not possible with a CCD technology. Instead a standard 0.7J..lmCMOS technology was used but photodetector structures for this technology are not well characterised. As such characterisation of several common photodiode structures was carried out which showed good responsitivity of the order of 0.3 AIW. Prior to fabrication on-chip, a hardware emulation system using a reprogrammable FPGA was built which implemented the centroiding algorithm successfully. Subsequently, the design was implemented as a single-chip CMOS solution. The fabricated optical centroid processor successfully computed and transmitted the centroids at a rate of more than 2.4 kHz, which when integrated as an array of tilt sensors will allow a data rate that is independent of the number of tilt sensors' employed. Besides removing the data bottleneck present in current systems, the design also offers advantages in terms of power consumption, system size and cost. The design was also shown to be extremely scalable to a complete low cost real time adaptive optics system

Study of efficient transmission and reception of image-type data using millimeter waves

Evaluation of signal processing and modulation techniques for transmission and reception of image type data via millimeter wave relay satellite

Single atom detection on an atom chip with integrated optics

The subject of this thesis is the miniaturization and integration of detectors for the detection of single rubidium atoms on an atom chip. For this purpose three different detectors were developed for atom detection by absorption or fluorescence: i) A fluorescence detector was realized by mounting a tapered lensed fiber perpendicular to a collection fiber. ii) An absorption detector was built by placing a multi-mode fiber in-line with a tapered lensed fiber. iii) A tunable cavity detector was built from two single mode fibers mounted on the chip surface. To mount the detectors on the planar surface of the atom chip retaining structures by means of lithographical techniques were developed. Those structures allow a very accurate and stable passive fiber alignment. To test the individual detectors an atomic ensemble of thermal rubidium atoms was prepared in a magneto-optical trap. Then the atoms were transferred into magnetic micro-traps of the atom chip and were guided to one of the detectors. Each integrated detector has been evaluated by several characterization measurements. With the fluorescence detector the highest single atom detection efficiency of 54\% was attained. Thereby it was possible to perform quantitative measurements for the magnetically guided atoms on a single atom level and to study fundamental properties of the confined atoms